Oil shortages have sent oil prices skyrocketing. Although this paints a dreary picture for many Americans, it means that production of oil from shale is becoming more and more economically feasible. However, it is not practical at present to use state-of-the-art retort apparatus on a truly economically feasible basis. While it is known that large amounts of rich oil shale are available to be mined right here in the United States, none of the prior art apparatus can continuously retort large amounts of the rich shale. One inventor, W. S. Bergen, realizing this deficiency in his own invention (#3,574,087), suggested mixing rich shale and lean shale to get an optimum medium oil content shale for his process. Of course such a requirement for carefully mixing input shale precludes full automatic operation and thus severely limits economic feasibility.
When rich shale is used, the vapors in the retort passage become saturated with oil. In many of the prior art units, these vapors rise up to the cooler shale ore, condense on this shale and cause the sticking together of shale, resulting in bridging and clinkering, finally clogging the retort.
The present invention overcomes this problem with these improvements:
First, all the shale in the retort passage is kept above the dew point, so the oil cannot condense on the shale;
Second, the retort passage is entirely gravity feed, with no moving parts to wear out or clog;
Third, the retort passage increases in cross sectional size as the shale is fed downward, thus precluding blockage by frictional engagement with the walls of a constant width or narrowing retort;
Fourth, there is a downward flow of air through the retort passage that keeps most vapor flowing from cooler shale to hotter shale, thus providing an additional feature to avoid oil condensation on the cooler shale;
Last, there are water cooled oil condensing gutters on the sides of the retort passage, separated from the shale, which remove product oil from the vapor while the vapor is still in the retort passage.
There are other reasons for clogging that makes prior art units not practical for the high through-puts necessary for economic feasibility. For example, one type of unit which has been proposed employs gas distributors within the retort where recycled shale gas is burned. These units, which are reported to represent one of the most feasible types which have been designed up to the present invention, are plugged up when clinkering and bridging occur in the area of the gas distributors. Also, the direct exposure of the shale to open flame reduces the yield from the apparatus. Another proposed retort used an inverted cone shaped retort with the oil shale being pushed in from the bottom and coke removed from the top. This unit operated satisfactorily in small sized units, but when built in larger sizes for more economically feasible production of oil from shale, it was found to have hot spots along the sides of the chamber.
Another major advantage of the present apparatus over prior art units is the method used for heating the shale up to retorting temperatures. Many of the prior art units do not even take advantage of the possibility of burning the retorted shale as fuel for the retort, and none take full advantage of the resultant heat. For example, in U.S. Pat. No. 2,434,815 to R. J. Shaw the shale is burned to make steam, and through a complex process heats the shale in the retort passage. On the other hand, in the present apparatus the gasses from the burning coke directly heat the heat exchange plate, which keeps the shale above the dew point, and also flow through the retort passage, picking up the oil laden vapor and carrying it out to a vapor condenser/separator.
Not only is the presently contemplated apparatus the most economically feasible, but also it is the most ecologically acceptable. A minimum amount of stack emission is produced and is easily controlled by electrostatic precipitators, scrubbers or any other state-of-the-art method of air pollution control. Water and ground Pollution is virtually non-existent, as this process uses no water other than the small amount of water used in equipment such as cooling towers and the generation of on-site steam which are not directly related to the actual retorting.
The present continuous feed inclined retort system combines the capability of handling very rich shale in a large daily capacity with the capability of operating without external energy sources, even on fairly lean shale, in an apparatus simpler in design and yet more economically feasible and ecologically acceptable than all known prior oil shale recovery units.
Other advantages, features and objects of the invention will become apparent from a consideration of the following detailed description and from the drawings.